WASHINGTON (AP) — Intelligence suggests the Syrian government has moved some of its chemical weapons in order to protect them, but the U.S. believes that the main sites remain secure, Defense Secretary Leon Panetta said Friday, indicating there are lingering questions about what exactly happened to some of the weapons.

It was the first time Panetta confirmed that U.S. officials believe there have been multiple "limited" movements of the chemical weapons, but he said Syrian officials were relocating them in order to better secure them.

"There has been intelligence that there have been some moves that have taken place. Where exactly that's taken place, we don't know," Panetta told reporters. "I don't have any specific information about the opposition and whether or not they've obtained some of this or how much they've obtained and just exactly what's taken place."

Asked specifically if there was any belief that the Iran's powerful Revolutionary Guard or the rebel forces have been able to get possession of any of the weapons, Panetta appeared to leave the door open to that possibility, saying he has no "firm information to confirm that that's taken place."

He said the U.S. has monitored the main sites and determined that they are still secure.

There have been ongoing concerns that the opposition forces battling the regime of Syrian President Bashar Assad or other militant forces in the country may get their hands on the weapons caches.

It is widely believed that Syria possesses extensive chemical and biological weapons stockpiles and it has threated to use them if the country comes under attack.

President Barack Obama has declared that the threat of chemical or biological warfare in Syria is a "red line" for the U.S., and has warned that the U.S. will not tolerate it if the weapons fall into the wrong hands. He said there would be enormous consequences if the U.S. sees any movement or use of the weapons.

Panetta was speaking at a news conference with Canadian Minister of National Defense Peter MacKay.